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Librenix: A look at the IBM mainframe as a massive Linux instance server

"I've written on this topic before but I keep running
into the same misconception: that the IBM mainframe is a
cost-effective platform for Linux because over 40,000 instances of
Linux have been shown to run concurrently on a modern mainframe.

That demonstration was effectively a gimmick. No, I don't
believe it was intended as a gimmick; only that it was widely
misconstrued and, therefore, became indistinguishable from a
gimmick in the media circus that resulted. It was depicted by the
media as a practical demonstration that one could replace 40,000
PC's running Linux with a single mainframe. Alas, that was surely
not the point of the demonstration.

Don't confuse a large number of 'logical' machines with physical
ones. If a Pentium III had the ability in hardware to subdivide
itself into thousands of functionally identical logical processors
you would be able to run thousands of Linux instances on that one
CPU. You probably see the problem that you would immediately
encounter: each Linux instance would have only a tiny fraction of a
percent of the PIII's processing power. Yes, you'll have thousands
of distinct running instances of Linux, but they will be very slow
when several of them try to do something cpu-intensive at the same
time."